Obtaining an urban residence permit, called a hukou, is possible only for those with deep pockets or top-notch connections, so struggling migrants live in a gray zone of pay-as-you-go medical care, dingy rented rooms and unregistered schools where the education is middling at best.

Under a system known as hukou, many rural workers can't access state-subsidized social services like education and health care unless they're officially registered in their new address after moving from the countryside.

China's household registration system and residency permits, known as "hukou," ties people to their original place of residence, essentially rendering migrant workers from the countryside illegal immigrants when they move to cities.

The system of registered permanent residence, known in China as the "hukou", is blamed for turning holders into virtual second-class citizens in areas where they have relocated in search of work and perpetuating the wealth divide.